1. Field of the Invention
The present invention relates to an improved power transmitting device in a rotating machine which is designed to absorb impact generated by a power intermittent, and more particularly to an electromagnetic clutch.
2. Description of the Prior Art
In a conventional electromagnetic clutch, for example that disclosed in Japanese Examined Utility Model Publication No. sho. 58-8997, three holes are provided on a stopper plate and cylindrical damper covers are respectively welded to positions on an outer surface of the stopper plate in which the holes are provided. Each of the damper covers is provided with a hole in the bottom portion thereof having the same diameter as a hole in the central portion thereof. In each of the damper covers, a damper rubber piece is embedded. A collar having a flange is inserted into the central portion of this damper rubber piece to fix an armature to the stopper plate through the holes of the respective damper covers and the holes formed in the stopper plate. The outside diameter of the collar is smaller than the inside diameter of each of the holes of the stopper plate and of the hole in each of the damper covers, allowing each of the collars to be displaced in the radial direction of the stopper plate and the damper covers. Consequently, an impact caused when the armature is attracted by a rotor can be absorbed. Conventionally, absorption can be accomplished in the above described manner.
The above-mentioned electromagnetic clutch according to the conventional technique, however, is defective in that when an excessive starting torque is exerted on the damper rubber pieces upon starting, the respective flanges press the damper rubber pieces in the direction in which they are attracted, and the end portions of the flanges undesirably bite into the damper rubbers while the damper rubber pieces disadvantageously pushed into the holes of the damper covers, reducing the durability of the damper rubber pieces and the durability of the electromagnetic clutch.
In addition, in the above-described electromagnetic clutch according to the prior art, about a further problem occurs in that when an excessive starting torque is applied to the damper rubber pieces upon starting, force in the rotating direction (torsional direction) of the electromagnetic clutch is inconveniently applied to the damper rubber pieces. As a result, the damper rubber pieces are seriously deformed, so that the durability of the damper rubber pieces is reduced and the durability of the overall electromagnetic clutch is severely reduced.